In the production of high gloss paper, a base sheet is coated with white pigment. White pigments include talc, clay, ground calcium carbonate (GCC) and precipitated calcium carbonate (PCC).
PCC has a key advantage over GCC in that smaller average particle sizes with moderate specific surface areas (SSA) are possible, whereas ultra ground CGG has (I) high energy costs for grinding and (ii) higher SSA in the final product due to solid particle morphology. Fine PCC, that is PCC with average particle size of below about 1.6 microns, as produced is too dilute in concentration to be used in paper coating. The need therefore exists to concentrate the aqueous slurry of PCC or remove water from the slurry to render the percent solids of the slurry about 65 weight percent or greater.
Numerous problems result when using vacuum dewatering equipment on calcium carbonate. For example, clogging of the vacuum dewatering machine occurs during paper production. Typically, the vacuum machine must be shutdown, and washed with water, in order to relieve clogging.
Machine downtime increases the overall cost of paper production. Similar problems have been experienced using dewatering technology that employs air-blow type cycles to dry calcium carbonate.
For example, when air-blow type machinery is employed to dewater calcium carbonate products having cake solids of greater than 65 percent and an average particle sizes of less than or equal to 1.6 microns, a more effective air-blow cycle for efficient dewatering of the calcium carbonated is required. Current air blow systems are inadequate at dewatering small average particle size calcium carbonate products to specific solids levels.
Therefore, what has been found to be novel and unanticipated by any prior art is a method for dewatering calcium carbonate slurries where cake solids and average particle size is important aspect of the final product.